In a Third Generation (3G) cellular system, such as the system 100 shown in FIG. 1, EU provides improvements to uplink (UL) data throughput and transmission latency. The system 100 includes a Node-B 102, an RNC 104 and a wireless transmit/receive unit (WTRU) 106.
As shown in FIG. 2, the WTRU 106 includes a protocol architecture 200 which includes higher layers 202 and an EU medium access control (MAC), (MAC-e) 206, used to support EU operation between a dedicated channel MAC, (MAC-d) 204, and a physical layer (PHY) 208. The MAC-e 206 receives data for EU transmission from channels known as MAC-d flows. The MAC-e 206 is responsible for multiplexing data from MAC-d flows into MAC-e protocol data units (PDUs) for transmission, and for selecting proper EU transport format combinations (E-TFCs) for EU transmissions.
To allow for EU transmissions, physical resource grants are allocated to the WTRU 106 by the Node-B 102 and the RNC 104. WTRU UL data channels that require fast dynamic channel allocations are provided with fast “scheduled” grants provided by the Node-B 102, and channels that require continuous allocations are provided with “non-scheduled” grants by the RNC 106. The MAC-d flows provide data for UL transmission to the MAC-e 206. The MAC-d flows are either configured as scheduled or non-scheduled MAC-d flows.
A “serving grant” is the grant for scheduled data. A “non-scheduled grant” is the grant for non-scheduled data. The serving grant is the power ratio that is converted to a corresponding amount of scheduled data that can be multiplexed, thus resulting in the scheduled data grant.
The RNC 104 configures non-scheduled grants for each MAC-d flow using radio resource control (RRC) procedures. Multiple non-scheduled MAC-d flows can be configured simultaneously in the WTRU 106. This configuration is typically performed upon radio access bearer (RAB) establishment, but may be reconfigured when necessary. The non-scheduled grant for each MAC-d flow specifies the number of bits that can be multiplexed into a MAC-e PDU. The WTRU 106 is then allowed to transmit non-scheduled transmissions up to the sum of non-scheduled grants, if multiplexed in the same transmission time interval (TTI).
Based on scheduling information sent in rate requests from the WTRU 106, the Node-B 102 dynamically generates scheduling grants for scheduled MAC-d flows. Signaling between the WTRU 106 and the Node-B 102 is performed by fast MAC layer signaling. The scheduling grant generated by the Node-B 102 specifies the maximum allowed EU dedicated physical data channel (E-DPDCH)/dedicated physical control channel (DPCCH) power ratio. The WTRU 106 uses this power ratio and other configured parameters to determine the maximum number of bits that can be multiplexed from all scheduled MAC-d flows into a MAC-e PDU.
Scheduled grants are “on top of” and mutually exclusive of non-scheduled grants. Scheduled MAC-d flows can not transmit data using a non-scheduled grant, and non-scheduled MAC-d flows can not transmit data using a scheduled grant.
The EU transport format combination set (E-TFCS) comprising all possible E-TFCs is known to the WTRU 106. For each EU transmission, an E-TFC is selected from a set of supported E-TFCs within the E-TFCS.
Since other UL channels take precedence over EU transmissions, the power available for EU data transmission on E-DPDCH is the remaining power after the power required for DPCCH, dedicated physical data channel (DPDCH), high speed dedicated physical control channel (HS-DPCCH) and EU dedicated physical control channel (E-DPCCH) is taken into account. Based on the remaining transmit power for EU transmission, blocked or supported states of E-TFCs within the E-TFCS are continuously determined by the WTRU 106.
Each E-TFC corresponds to a number of MAC layer data bits that can be transmitted in an EU transmission time interval (TTI). Since there is only one MAC-e PDU per E-TFC that is transmitted in each EU TTI, the largest E-TFC that is supported by the remaining power defines the maximum amount of data, (i.e., the number of bits), that can be transmitted within a MAC-e PDU.
Multiple scheduled and/or non-scheduled MAC-d flows may be multiplexed within each MAC-e PDU based on absolute priority. The amount of data multiplexed from each MAC-d flow is the minimum of the current scheduled or non-scheduled grant, the available MAC-e PDU payload from the largest supported TFC, and the data available for transmission on the MAC-d flow.
Within the supported E-TFCs, the WTRU 106 selects the smallest E-TFC that maximizes the transmission of data according to the scheduled and non-scheduled grants. When scheduled and non-scheduled grants are fully utilized, available MAC-e PDU payload is fully utilized, or the WTRU 106 has no more data available and allowed to be transmitted, MAC-e PDUs are padded to match the next largest E-TFC size. This multiplexed MAC-e PDU and corresponding TFC are passed to the physical layer for transmission.
The serving and non-serving grants specify the maximum amount of data that can be multiplexed from specific MAC-d flows into MAC-e PDUs each EU TTI. Since the scheduled grants are based on the E-DPDCH/DPCCH ratio, the number of data bits allowed to be multiplexed per MAC-e PDU can not be explicitly controlled only to allow certain sizes which match the limited number of data sizes of the supported E-TFCs within the E-TFCS.
The remaining transmit power for EU data transmission determines the list of supported E-TFCs within the E-TFCS. Since the supported E-TFCs are determined from a limited number of E-TFCs in the TFCS, the granularity of allowed MAC-e PDU sizes will not allow for all possible MAC-d flow and MAC-e header combinations. Therefore, since the amount of MAC-d flow data allowed by the grants to be multiplexed into a MAC-e PDU will frequently not match the size of one of the supported E-TFCs, padding will be applied to the MAC-e PDU to match the smallest possible E-TFC size within the list of supported E-TFCs.
It is expected that when EU cells are operating at maximum capacity the MAC-e PDU multiplexing is frequently limited by the serving and non-serving grants, and not limited by the largest supported E-TFC or the WTRU EU data available for transmission. In this case, depending on the granularity of specified E-TFCs within the E-TFCS, padding required to match the selected E-TFC may exceed the multiplexing block size of MAC-d flow data including associated MAC-e header information. In this case, the effective data rate is unnecessarily reduced from what is allowed by the selected E-TFC and the physical resources required for its transmission.
FIG. 3 illustrates a MAC-e PDU 300. A MAC-e PDU header 302 and MAC-d flow data 304 allowed by scheduling and non-scheduling grants are multiplexed. Among a set of supported E-TFCs, the WTRU 106 selects the smallest E-TFC from a list of supported E-TFCs that is larger than MAC-e PDU header 302 and MAC-d flow data 304. Padding 306 is then applied to the MAC-e PDU to match the selected E-TFC size. However, the padding 306 may exceed the multiplexing block size of MAC-d flow data. In this case, physical resources used in the EU transmission are under utilized and the effective WTRU data rate is unnecessarily reduced. Accordingly, it is desirable to have alternate approaches to multiplexing EU data.